1. Field of the Invention
The present invention is directed to a conveyor device used for instance on a blank folding machine, which conveyor device includes a belt conveyor and at least one vacuum chamber which extends parallel to the direction of movement of the belt conveyor.
2. Prior Art
Presently known conveyor devices for blank folding machines, which fold boxes or carton blanks prior to assembly, generally consist of one or more conventional belt conveyors operated jointly with at least one vacuum chamber. The vacuum chamber is positioned to extend in a direction parallel to the direction of movement of the conveying surface of the belt conveyor with its top surface lying in the plane of the conveying surface which is transporting the blank. In most cases, the vacuum chamber is adjustable to various positions relative to the belt path so that a suction can be applied either on specific areas of a blank as required during a folding operation or at specific points in the blanks path of travel on the belt conveyors. The conveyor device with the vacuum chambers has the advantages of enabling the application of a holding pressure to firmly hold a blank while various folding operations are accomplished for example turning over a flap or tab of the blank.
However, in the presently known devices, when more than one suction or vacuum chamber are utilized either in side-by-side relation or at different positions along the path of the conveyor belt, they are connected to a single or common vacuum source and problems occur with maintaining a sufficient suction on the blank during each operation. This is due to the fact that once a blank moves over or off one of the vacuum chambers to uncover its openings, the vacuum system is vented to the ambient atmosphere. The venting of one chamber reduces the amount of vacuum applied to all of the other chambers connected to the same vacuum source. The reduction of the vacuum in the other chambers results in a reduction in the suction or vacuum pressure that can be applied for holding a blank during other operations of the blank folding device.
As mentioned above, each of the vacuum chambers on a device are normally fed from a single vacuum source and, therefore, the arrangement of the vacuum chambers on a folding machine limits the machine to operate on blanks having an outline which minimizes the loss of vacuum or suction pressure due to an uncovered vacuum chamber. To solve the problem of a loss of vacuum due to uncovering of the openings of one of the vacuum chambers, it has been suggested to provide each of the vacuum chambers with an electro-magnetic valve arrangement which would operate to disconnect the chamber from the vacuum source once its openings were uncovered by the passing of a blank. However, this solution to the problem increases the expenses for manufacturing the device and thus increases the cost of the device.